Concept design sketches I did when designing Kuiper the frog. He was half-way being made as a cartoon version of a friend of mine, so he helped decide on the final design. He liked the longer legs, otherwise Kuiper would have been stubby like the upper-right!
This image is his final design, and comparing to Nicolai in height.
Here are some even older images in the design process. It took a long time and a lot of sketches for me to be happy with the way I drew frogs.